Electronically commutated motors operate with a stator winding that has a small number of phases. The motors principally used have one, two, or three phases. These phases can have power supplied to them in different ways depending on the type of electronics; supplying power via a full bridge circuit offers particular advantages.
With a full bridge circuit, steps must be taken to ensure that a short circuit does not occur in the full bridge. There are numerous circuits for this, for example the circuit according to U.S. Pat. No. 4,376,261, von der Heide, et al., which is based on the principle of creating a small gap between two control pulses. When the full bridge is controlled via a microprocessor (μP), corresponding current off-times can thus be “built into” the program, ensuring that upon commutation the one transistor switches off, then there is a delay of, for example, 50 μs, and only then is the other transistor switched on. A prerequisite for this, however, is that a microprocessor be used, and this is too expensive for many applications. The current off-time of, for example, 50 μs must furthermore be made so long that is sufficiently long under all operating conditions, with the result that, especially at higher rotation speeds, power output may be “wasted” because the current off-time could be shorter under many operating conditions.